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Clubroot is a soil-borne disease of cruciferous crops, including <i>Brassica rapa</i> ssp. <i>pekinensis</i>, and causes substantial yield losses. In an attempt to develop clubroot-resistant <i>B. rapa</i> cultivars, we investigated the role of a root-abundant expansin-like B1 <i>(EXLB1)</i> during <i>Plasmodiophora brassicae</i> inoculation. The histochemical analyses of infected transgenic reporter lines showed a role for <i>BrEXLB1</i> in disease response as early as 3 dpi. The transgenic overexpression of <i>EXLB1</i> in <i>B. rapa</i> conferred disease-sensitive phenotypes and was comparable to non-transgenic controls at 30 dpi. In contrast, the heterogeneous population of antisense <i>BrEXLB1</i>-overexpressing lines conferred disease resistance against highly pathogenic <i>P. brassicae</i> race 2 inoculations under greenhouse conditions. Additionally, we profiled the relative expression of 32 other <i>BrEXPs</i> in wild-type seedlings, sampled on different days (1–10) after inoculation using qRT-PCR. The results indicate that the expression pattern of most <i>BrEXP</i> genes was significantly altered during different infection times, suggesting their participation in clubroot responses. In particular, the expressions of <i>EXPA20</i>, <i>EXPA21</i>, and <i>EXPA34</i> were consistently downregulated, while the expression of <i>EXPA5</i> was upregulated (log₂FC ≥ 2) compared to controls. Altogether, our study showed that <i>BrEXPs</i> participate in clubroot disease response, and their genetic manipulation is likely to provide clubroot disease resistance.